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Radiometric Chronology of Neh–nar Glacier, Kashmir

  • V. N. Nijampurkar (a1), N. Bhandari (a1), C. P. Vohra (a2) and V. Krishnan (a2)

Abstract

Surface and core samples of Neh–nar Glacier in the Kashmir Valley have been analysed for the radionuclides 32Si. 210Pb, 40K, and 137Cs. The lateral and vertical profiles (at an altitude of about 4 140 m) reveal:

(1)32Si activity decreasing slowly from the accumulation zone to 4 050 m altitude and then abruptly towards the snout.

(2)Five zones of alternating high and low 210Pb activity in the surface samples.

(3)An horizon at between 2 and 3 m depth containing 210Pb activity above natural levels. This horizon is also associated with 137Cs and a maximum in total ß activity.

The ice samples have been dated on the basis of a simplified two–component model, the “fresh“contribution determined by 2l0Pb and the old component by 32Si. The following conclusions can be drawn from these observations:

(1)The model age of the snout ice is c. 850 years.

(2)The average rate of ice movement in the lower glacier is about 2 m/year, which compares well with the annual movement rate of 2.65 m/year observed since 1974.

Résumé

Chronologie du Neh–nur Glacier, Kashmir, par radiomètrie. Des échantillons prélevés en surface et par carottage dans le Neh–nar Glacier, dans la vallée du Kashmir, ont été analysés pour leur teneur en radionuclide 32Si. 2l0Pb. 40K, et 137Cs. Les profils latéraux et verticaux (à une altitude d’environ 4 140 m) révèlent:

(1)Une activité du’ 32Si décroissant lentement depuis la zone d’accumulation jusqu’à l’altitude de 4 050 m puis s’effondrant brusquement jusqu’à la langue.

(2)Cinq zones présentant alternativement des activités fortes et faibles en 2l0Pb dans les échantillons de surface.

(3)Un horizon entre 2 et 3 m de profondeur contenant une activité en 2l0Pb supérieure aux niveaux naturels.

Cet horizon est également associé à du l37Cs et à un maximum d’activité beta totale.

En se basant sur un modèle simplifié à deux composantes, ou la contribution de la glance “fraîche” est déterminée par 2l0Pb et la composante ancienne par 2Si, on a pu dater les échantillons de glace. De ces observations on a putirer les conclusions suivantes:

(1)L’âge théorique de la glace du front est d’environ 850 ans.

(2)La vitesse moyenne de la glace dans le bas du glacier est d’environ 2 m par an, ce qui cadre bien avec la vitesse réelle de 2,65 m/an observée depuis 1974.

Zusammenfassung

Radiometrische Chronologie des Neh–nar Glacier, Kashmir. Proben von der Oberfläche und aus Bohrkcrnen des Neh–nar Glacier im Kashmir–Tal wurden auf die Radionukleide 32Si, 210Pb, 40K, und 137Cs untersucht. Die Horizontal und Vertikalprofile (in einer Höhe von etwa 4 140 m) geben folgendes Bild:

(1)Die 32Si–Aktivität nimmt erst langsam, dann abrupt von der Akkumulationszone in 4 050 m Höhe zur Zunge hin ab.

(2)Die Oberflächenproben weisen 5 Zonen von wechselweise hoher und niedriger 210Pb–Aktivität aus.

(3)Ein Horizont in 2 bis 3 m Tiefe weist eine 2l0Pb Aktivität über normalem Niveau auf. Dieser Horizont ist auch mit 137Cs und einem Maximum in der Gesamt–Beta–Aktivität verbunden.

Auf der Grundlage eines Zwei–Komponenten–Modells, nämlich des “frischen” Beitrags durch 210Pb und der allen Komponente durch 32Si, wurden die Eisproben datiert. Aus diesen Beobachtungen können folgende Schlüsse gezogen werden:

(1)Das Modkl Aller des Zungcncises beträgt elwa 850 Jahre.

(2)Die miniere Jahresbewegung des Eises im unteren Teil des Gletschers ist schätzungsweise 2 m pro Jahr, was gut mit dem seit 1974 beobachteten Wert von 2,65 m pro Jahr zusammenstimmt.

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References

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Radiometric Chronology of Neh–nar Glacier, Kashmir

  • V. N. Nijampurkar (a1), N. Bhandari (a1), C. P. Vohra (a2) and V. Krishnan (a2)

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